The adjustment of the wheels and wheel axles of a motor vehicle is an intricate but important question, as the driving characteristics of the vehicle will depend greatly on how wheels and axles are aligned and adjusted. When driving straight ahead the rotational planes of the front wheels are inclined in various ways in relationship to a vertical plane, more particularly to a plane parallel with the vertical symmetrical plane of the vehicle. Viewed directly from above the wheels show "toe-in" or "toe-out", that is to say they are set at a slightly oblique angle to the direction of travel, whereas, when viewed directly from the front they tilt somewhat, preferably outwards, in relation to said vertical plane, by an angle designated as the wheel inclination or "camber". How the steering pivot pins or "king pins" of the front wheels are inclined in various vertical planes also have influence on the driving, and for a more detailed description of the wheel alignment angles in the front axle and suspension assembly of a motor vehicle reference is had to U.S. Pat. No. 4,823,470, where these conditions are discussed at length. In this patent there are also disclosed methods for determining accurately the magnitude of the angles concerned.
The invention has for its object to make available a simplified procedure for measuring, while maintaining accuracy, the most important one of the wheel alignment angles, viz., the said wheel inclination or camber. The object is achieved by providing a straight reference member, such as a rod or bar, which is placed on a base surface in front of and close to the wheels. One end of the reference member constitutes a reference pin which is parallel to the base surface and substantially parallel to a line extending between the wheel centers. The camber angle is determined by measuring the difference between the inclination to the true horizontal plane of the reference pin and the inclination to the true horizontal plane of a wheel pin. Further an arrangement for the implementation of the above method includes a measuring body which pivotably carries a plate-like bridge, with the pivot axis of the bridge being perpendicular to a guide groove located at the underside of the measuring body. The bridge pivots by means of a screw spindle mechanism operable by a knob. The knob is adapted to display the angle of the change in inclination of the bridge.
In order to exercise the invention it is necessary that the direction of the axis of rotation of the wheels subjected to measurement be established accurately, and a very simple so called centering device for this purpose is disclosed in U.S. Pat. No. 4,011,659, to which reference is also made.